Endoscopic instrument with disposable auto-regulating heater

ABSTRACT

An instrument for use in endoscopic surgery is provided. The instrument has a reusable shaft to which a disposable working tip can be removably attached. The disposable working tip has a working surface for providing hemostasis at an auto-regulated temperature. The working surface may include a tapered edge for providing thermally-enhanced cutting and a non-stick coating for operating the instrument at low auto-regulation temperatures. The instrument is capable of being used for a wide variety of endoscopic surgical procedures.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation, of application Ser. No. 07/960,471, filed Oct.9, 1992, now abandoned, entitled ENDOSCOPIC INSTRUMENT WITH DISPOSABLEAUTO-REGULATING HEATER, which is a continuation-in-part of applicationSer. No. 07/877,476, filed May 1, 1992, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to instruments for use in endoscopic surgery.More particularly, this invention relates to instruments with adisposable auto-regulating heater for use in endoscopic surgery.

Minimally invasive surgery such as endoscopic surgery allows for majorsurgical operations to be performed with reduced pain and disabilityrelative to conventional "open" surgery. In performing endoscopicsurgery, the surgeon does not cut a large incision through the body wallto obtain access to the tissue requiring treatment. Instead, anendoscope, typically a miniaturized video camera, and certainspecially-designed surgical instruments are inserted through a trocartube or similar device. Trocar tubes, typically having a 5 mm to 10 mminside diameter, produce only a small opening. The image provided by theendoscope is displayed on a large video screen or other type of monitor,thereby affording the surgeon enhanced visual control of thespecially-designed instruments.

Endoscopic surgery is possible whenever a small optical instrument(endoscope) and miniaturized operating instruments can be inserted intothe body cavity or other anatomical space. Such miniaturized operatinginstruments have been developed for endoscopic surgery in the abdomen("laparoscopy"), in the chest ("thoracoscopy") and in joints("arthroscopy").

In performing both "open" and endoscopic surgical procedures, thesurgeon must control bleeding that occurs when tissues are incised. Suchbleeding obscures the surgeon's vision, reduces precision, and oftennecessitates slow and elaborate procedures to perform the surgery.

Controlling flow of blood from incised tissue is readily accomplished in"open" surgical procedures, because the surgeon can directly touch andmanipulate the various tissues. Bleeding from incised tissue iscontrolled by blotting or evacuating the accumulating blood. This stepof removing the blood permits visual observation of the vessels forclamping or tying of those vessels to inhibit further blood loss.

In performing endoscopic surgery, the surgeon forgoes direct manualaccess to the tissue being operated upon. Thus, traditional means ofphysically controlling bleeding (i.e., clamping and tying) areunavailable. Other techniques must then be employed to control bleedingduring the surgical procedure. One such technique, which was firstemployed in "open" surgical procedures, is to thermally heat thebleeding tissue. Such thermal heating reduces the tendency of severedtissue to bleed.

For "open surgery" it is known to provide surgical scalpels which employa blade with an adjacent resistive heating element. The resistiveheating element provides thermally-enhanced cutting, in addition tohemostasis, when electrical current is passed through the element.Although such resistive elements can be readily brought to a suitablyhigh and constant temperature in air prior to contacting tissue, theyrapidly cool when brought into contact with tissue. During "open"surgery, non-predictable and continually varying portions of the bladecontact the tissue as it is being cut. As the blade cools, its abilityto cut tissue and provide hemostasis becomes markedly less effective.Furthermore, tissue tends to adhere to the blade. If additional power isapplied by conventional means to counteract this cooling, the additionalpower may be delivered to the uncooled portions of the blade, thusresulting in tissue damage and blade destruction.

Shaw U.S. Pat. No. 4,185,632 shows an improved surgical cuttinginstrument in which the temperature of the cutting portion of the bladeis self-regulating. Radio frequency electrical currents maintain thetemperature within an elevated preselected temperature range. Thesecurrents flow within variable skin depths in an electrical conductordisposed near the cutting edge of the blade. This variable skin deptheffect produces self-regulation of the blade temperature.

In addition to the ability to provide hemostasis, and to remotely cutand dissect tissue, endoscopic surgery requires the use of instrumentsthat reduce adherence of tissue to the instrument. Coagulum buildup andsticking limits the usefulness of the instrument and may causeundesirable tissue damage and bleeding. Also, the adherence of tissue tosuch surgical instruments limits the surgeon's control of theinstrument.

It would therefore be desirable to provide a low cost hemostaticinstrument for endoscopic surgery which has the ability to preciselycontrol the location and quantity of thermal energy which is deliveredto tissue.

It would also be desirable to provide an endoscopic instrument that hasthe ability to provide localized and precise thermally-enhanced cuttingof tissue.

It would further be desirable to provide an endoscopic instrument whichreduces the adherence of tissue and coagulum to the instrument so as toreduce tissue damage associated with such adherence and to maintain goodthermal power delivery between the heating means and the tissue byreducing the thermal impedance associated with tissue or coagulum buildup on said heating means.

In addition to the above, it would still further be desirable to providean endoscopic instrument that is capable of being used for a widevariety of endoscopic surgical procedures. Thus, it would also desirableto provide an endoscopic instrument that has a reusable universal handlewhich is capable of accommodating a wide variety of disposable workingsurfaces wherein a used working surface can be easily removed from thehandle and replaced with a new or differently shaped working surface.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of this invention to provide alow cost hemostatic instrument for endoscopic surgery which has theability to precisely control the location and quantity of thermal energythat is delivered to operative tissue.

It is another object of this invention to provide an endoscopicinstrument that has the ability to provide localized and precisethermally-enhanced cutting of tissue.

It is a further object of this invention to provide an endoscopicinstrument which reduces the adherence of tissue and coagulum to theinstrument so as to reduce tissue damage associated with such adherenceand to maintain good thermal power delivery between the heating meansand the tissue by reducing the thermal impedance associated with tissueor coagulum build up on said heating means.

It is a still further object of this invention to provide an endoscopicinstrument that is capable of being used for a variety of endoscopicsurgical procedures. Thus, it is an object of this invention to providean endoscopic instrument that has a reusable universal handle which iscapable of accommodating a wide variety of disposable working surfaceswherein a used working surface can be easily removed from the handle andreplaced with a new or different one.

In accordance with the present invention there is provided a disposableworking tip for use in endoscopic surgery. The disposable working tip isadapted to be disposed from an end of a reusable elongated shaft andincludes: a disposable heating element having first and secondelectrodes adapted to be removably attached to the end of the reusableelongated shaft and having a working surface for contacting tissue,wherein the working surface is maintained at an auto-regulatedtemperature, the heating element comprising a material having a skindepth responsive to the temperature of the heating element and thatdecreases as the temperature of the element falls below theauto-regulated temperature.

The working surface of the disposable heating element may also includean optional tapered edge for thermally-enhanced cutting of tissue and anelectrically insulating non-stick coating to reduce coagulum buildup.

The above disposable working tip may also include an end cap having apassageway therethrough adapted to permanently hold the disposableheating element; and an engagement means disposed on the end cap forremovably attaching the disposable working tip to the end of thereusable elongated shaft.

In accordance with the present invention, there is also provided aninstrument for use in endoscopic surgery comprising the above disposableworking tip in conjunction with a reusable elongated shaft having aproximal end and a distal end, the proximal end of the shaft having apair of electrical terminals adapted to be coupled to a power supply.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention willbe apparent upon consideration of the following detailed description,taken in conjunction with accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 is a perspective view, partly in section, of endoscopic surgicalapparatus constructed in accordance with the principles of the presentinvention;

FIG. 2 is a cross-sectional view of the endoscopic instrument of FIG. 1,taken along line 2--2 of FIG. 1;

FIGS. 3A and 3B are illustrative cross-sectional views of heatingelement 12 of FIGS. 1 and 2, taken along line 3--3 of FIG. 2, attemperatures slightly below and above the auto-regulation temperature,respectively;

FIG. 4 is a cross-sectional view similar to FIG. 3, of an alternativedual-metal embodiment of the endoscopic instrument of the presentinvention;

FIG. 5 is a side view a dual-metal endoscopic instrument of the presentinvention incorporating a serpentine-shaped heating element;

FIG. 6 is a plan view, partly in section, of the endoscopic instrumentof FIG. 5, taken along line 6--6 of FIG. 5;

FIGS. 7A and 7B are, respectively, plan and elevation views of analternative embodiment of the present invention incorporating amonolithic heating element;

FIGS. 8A and 8B are, respectively, plan and elevation views of anendoscopic instrument constructed as shown in of FIGS. 7A and 7B,further incorporating the optional tapered thermally-enhanced cuttingedge of the present invention;

FIGS. 9A and 9B are, respectively, plan and elevation views of anendoscopic instrument similar to that of FIGS. 8A and 8B, furtherincorporating the optional non-stick coating of the present invention;

FIG. 10A is a perspective view of the distal end of an endoscopicsurgical instrument having a disposable working surface constructed inaccordance with the principles of the present invention;

FIG. 10B is a perspective view of the distal end of the endoscopicsurgical instrument of FIG. 10A prior to attachment of the disposableworking surface to the instrument shaft;

FIG. 11 is a detailed perspective view of the distal end of the reusableinstrument shaft of FIG. 10B;

FIG. 12A is a cross-sectional view of the disposable endoscopicinstrument of FIG. 10B, taken along line 12A--12A of FIG. 10B, duringattachment of the disposable working surface to the instrument shaft;

FIG. 12B is a cross-sectional view of the disposable endoscopicinstrument of FIG. 10A, taken along line 12B--12B of FIG. 10A;

FIG. 13A is an elevation view of a preferred embodiment of an electrodecontact made in accordance with the present invention; and

FIG. 13B is a plan view of the electrode contact of FIG. 13A.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, an illustrative embodiment of endoscopicinstrument 10 of the present invention is described. The working surfaceof this instrument may be used for causing hemostasis of incised tissueor for directly coagulating small tissue masses, either with or withoutsimultaneously incising the tissue. Endoscopic instrument 10 includes anelongated shaft 18 having proximal and distal ends. Elongated shaft 18may be either flexible or rigid, depending upon the intendedapplication. A working end comprising heating element 12 is disposedfrom the distal end of elongated shaft 18, while a handle (not shown)for facilitating manipulation of the instrument is disposed from theproximal end of elongated shaft 18. Electrical leads 14 and 16 extendboth to the handle, where they are then connected to power source 9, andto heating element 12 on the distal end of elongated shaft 18.

Endoscopic instrument 10 works as follows. Power source 9 provides analternating current (AC) electrical potential to terminals 13 and 15,respectively, of heating element 12 through electrical leads 14 and 16.In response the imposed electrical potential, an electrical current isconducted through heating element 12. That current results in jouleanheating, which raises the temperature of heating element 12 above bodytemperature (i.e., approximately 37° C.) to facilitate hemostasis andoptionally permit thermally-enhanced cutting of tissue.

The present invention provides auto-regulation of the temperature ofheating element 12. This self-regulating temperature feature resultsfrom constructing heating element 12 of a ferromagnetic material, orother material which undergoes a similar transition in currentconduction properties when the temperature of the material varies. It isknown that in such materials an AC current is confined to a regionadjacent the surface of the material. This phenomena is commonly calledthe "skin effect." The current density is generally greatest at thesurface and decreases in magnitude further into the material where theelectric field approaches zero. The depth at which the skin effectcurrent is reduced to about 37 percent of its surface value is referredto as the "skin depth" and is a function of the electrical resistivity,the magnetic permeability of the material conducting the current, andthe frequency of the applied alternating electric potential. It is knownthat the skin depth T_(SD), in centimeters, can be generally representedby the equation:

    T.sub.SD =(4×10.sup.3)sqrt(rho/[uf])

where rho is electrical resistivity in ohmcentimeters, u is relativemagnetic permeability, and f is frequency in Hertz.

Ferromagnetic materials such as iron, nickel, cobalt, and their alloys,exhibit large changes in relative permeability as the temperature goesthrough a transition point called the "Curie" point. Because therelative permeability changes in response to the temperature of thematerial, the associated skin depth also changes, and therefore theamount of current conduction through the skin layer undergoes atransition near the Curie point. This transition in current conductionproperties is used, as described hereinafter, to achieve auto-regulationof the temperature of heating element 12.

An auto-regulated endoscopic instrument is obtained in accordance withthe present invention by causing a radio frequency (RF) current to flowin heating element 12. Heating element 12 may be composed of aferromagnetic material or the like and uses the skin effect of thematerial to auto-regulate the temperature of the heating element.Heating element 12 is constructed of a material having it's currentconduction transition at or near the auto-regulation temperature desiredfor the particular endoscopic surgical application. When heating element12 is heated so that when a working surface of heating element 12contacts tissue, that region of the heating element cools below thetransition temperature. In response to the local temperature drop in theheating element, the associated skin depth responsively decreases as aresult of the Curie transition in the heating element material. Thereduced skin depth in turn results in an increase in local powerdissipation, so that the temperature automatically tends to increasetowards the auto-regulation temperature. Accordingly, the presentinvention uses the skin depth effect of the heating element material tomaintain the working surface of the endoscopic instrument substantiallyat the auto-regulated temperature throughout the range of conditionsencountered during surgery.

For example, for many iron-nickel alloys the Curie transition occurs atabout 450° C., above which the relative permeability is near unity.Below about 450° C., the relative permeability is high, perhaps 100 to1000, for the magnetic field strengths suitable for use in endoscopicsurgical instruments. Thus, when the local temperature of a heatingelement constructed of this material falls below about 450° C., due tolocal cooling of the heating element when it comes into contact withcool tissue, the associated skin depth decreases more than 10 to 1. Thedecrease in skin depth results in an increase in local power dissipationand, thus, an increase in heating to provide auto-regulation of theheating element temperature.

In accordance with the present invention, heating element 12 may becomposed of a ferromagnetic material or other material which undergoes asimilar transition in current conduction properties, as the temperatureof the material varies through the desired auto-regulation temperature,as discussed above. Preferably, heating element 12 is composed of analloy of nickel and iron. Examples I and II, provide illustrativeembodiments wherein the auto-regulation temperature is varied by varyingthe percentage of nickel and iron present in heating element 12.

Example I

For an auto-regulation temperature of approximately 315° C. at 1.8megahertz, the alloy may be approximately 42% nickel and 58% iron. Suchan alloy is available as LOW EXPANSION ALLOY 42, from CarpenterTechnology Corporation of Reading, Pa., and has the followingcharacteristics: unannealed, a hardness of approximately 91 Rockwell B,a tensile strength of approximately 98.5 ksi, an electrical resistivityat 23° C. of approximately 373 Ohms-cir mil/foot and a coefficient ofthermal expansion of approximately 3.1 (IN/IN F×10-6) from approximately77° to 700° F. Applicant has obtained satisfactory auto-regulationperformance with devices constructed of this alloy wherein the workingend of the heating element was approximately 18 mils (0.46 mm) thickwith a thermostat cold finish.

Example II

For an auto-regulation temperature of approximately 550° C. at 1.8megahertz, the alloy may be approximately 51% nickel and 49% iron. Suchan alloy is available as GLASS SEAL 52, also from Carpenter TechnologyCorporation of Reading, Pa., and has the following characteristics:unannealed, and with a coefficient of thermal expansion of approximately10.0 (IN/IN C×10-6) from approximately 25° to 550° C. Applicant hasobtained satisfactory performance with devices constructed of this alloywherein the working end of the heating element was approximately 20 mils(0.51 mm) thick.

After the heating element material has been selected, whether or notcontaining nickel or iron as in Examples I and II above, the heatingelement may then be configured into a variety of shapes, only one ofwhich is shown in FIGS. 1 and 2. Of course, the particular shape desireddepends upon the application of the particular endoscopic instrument.

In accordance with another feature of the present invention, it isdesirable that the cross-sectional dimensions of heating element 12 bechosen to allow the electrical conductance of heating element 12 tochange by at least a factor of 4 to 5 as the temperature of the workingsurface varies near the auto-regulation temperature. This feature of thepresent invention is illustrated by FIGS. 3A and 3B.

As shown in FIG. 3A, when the working surface temperature is slightlybelow the auto-regulation temperature, current 12a is confined toconduct in a region defined by the skin depth T_(SD) of heating element12. In accordance with the present invention, it is desirable thatthickness T_(E) of heating element 12 be approximately eight to tentimes the skin depth T_(SD), so that as the temperature of heatingelement 12 varies near the auto-regulation temperature, the electricalconductance of the element changes by a factor of about four to five. InFIG. 3B, where the heating element is at a working surface temperatureslightly in excess of the auto-regulation temperature, electricalcurrent 12b conducts throughout substantially the entire cross sectionof heating element 12 because the skin depth is then greater than halfof the thickness T_(E) of heating element 12. Thus, the effectiveelectrical conductance of heating element 12 increases by a factor offour to five as it varies near the autoregulation temperature, as shownin FIGS. 3A and 3B.

After the shape and cross-sectional dimensions of heating element 12 arechosen, heating element 12 may be constructed using any method whichproduces geometrical dimensions that are consistent with the desireddesign tolerances of the working surface. For example, such methodsinclude electric-discharge machining (EDM), blanking and chemicalmilling.

Heating element 12 is affixed to the distal end of elongated shaft 18 bypotting material 19, which electrically isolates heating element 12 andelectrical leads 14 and 16 from elongated shaft 18. Potting material 19should, in addition, be suitable for use in the temperature rangeexperienced by heating element 12. Furthermore, it is desirable thatpotting material 19 be able to withstand typical conditions encounteredin steam-sterilization procedures and have a viscosity that would allowit to be placed into the inner portion of elongated shaft 18.Accordingly, the potting material may be comprised of plastic, ceramic,silicone or epoxy-based materials.

Elongated shaft 18 has a diameter compatible with minimally invasivesurgery, for example, standard trocar tube inside diameters of 5 or 10mm, and a length that allows a surgeon to perform an endoscopicprocedure, for example, 13 inches. Preferably, elongated shaft 18 ismade of a high thermal conductivity material so as to dissipate (i.e.,distribute over the full length of said elongated shaft) that heat whichconducts from heating element 12 located at the distal end of the shaft.This feature reduces the potential that non-targeted tissue will besubjected to high temperatures that might cause damage.

For example, elongated shaft 18 may be constructed of copper or the likeand be plated with chrome on its outer surface. The chrome platingprovides a cosmetic dull-mat finish to the copper, which would normallyotherwise oxidize, and facilitates conventional steam-sterilizationprocedures.

An additional feature of the present invention is that a portion ofelongated shaft 18 near the distal end may be flexible so as to permitinsertion of the instrument within a patient's curved passageway.Alternatively, the flexible portion may extend to the proximal end sothat the elongated shaft may be inserted into a circuitous passageway,for example, an intestinal tract. Such a shaft allows the workingsurface of instrument 10 to reach remote treatment sites, e.g., sitessome distance beyond the entrance to the colon.

Electrical leads 14 and 16, which are connected to power source 9,should be capable of delivering the necessary AC current to heatingelement 12 with low electrical power loss. To avoid behavior associatedwith the skin effect, electrical leads 14 and 16 may each be composed ofmultiple strands of wire, wherein the individual strands are insulatedfrom each other. The insulation allows AC current to flow through eachindividual strand but not between strands. A suitable wire is availableas TYPE 2 LITZ WIRE (5×16×40), from Cooner Wire of Chatsworth, Calif.This particular wire is composed of 5 groups of 16 strands (i.e., atotal of 80 strands), wherein each strand, which are insulated from eachother, is of type 40 AWG.

In accordance with another feature of the present invention, when it isdesired to operate the endoscopic instrument below the temperature rangeof 450°-500° C., heating element 12 may also be coated with anelectrically-insulating "non-stick" coating. Such a coating reduces theaccumulation of coagulum on the working surfaces of heating element 12when operated at low temperatures. The application of such coatings tosurgical instruments, including a description of preferred coatings forthe present invention, are discussed in Shaw et al. U.S. Pat. No.4,848,337, which is hereby incorporated by reference in it's entirety.This patent describes an abherent coating for reducing the adherence oftissue to a surgical instrument for incising and causing hemostasis.Such coating includes materials selected from the group consisting ofsilicones, polydimethyisiloxanes, fluoride-metal composites andfluorocarbon polymers.

If a non-stick coating is desired, the coating may, more preferably, beeither a fluorine-containing mixture, such as polytetrafluoroethylene(PTFE), or a fluorotelomer-based mixture. In particular, the coating maybe either of type XYLAN® 8110/870 Black, available from WhitfordCorporation of West Chester, Pa., which is PTFE-based, or type VYDAX®1000 FLUOROTELEMER DISPERSION, available from E. I. du Pont de Nemours &Co., Inc., of Wilmington, Del., which is a fluorotelomer based-mixture.VYDAX® is preferred for longer-lasting applications where the surgicalinstrument will be reused multiple times. Furthermore, the VYDAX®thickness should preferably be in the range of approximately 0.3 to 0.4mil (0.0075 to 0.01 mm).

An important consideration for endoscopic "cutting" instruments is toreduce the exposure of non-operative tissue to surgically sharp edges.During manipulation of endoscopic instruments, inadvertent contacting oftissue might result in unwanted cutting (and associated bleeding).Hence, the endoscopic "cutting" instrument constructed in accordancewith the present invention is "sharp" only when the cutting instrumentis activated.

In accordance with the present invention, heating element 12 of FIGS. 1and 2 may include a tapered edge 11, which is not surgically sharp atbody temperature, but is able to cut tissue when heating element 12 isenergized. A cross-sectional view of tapered edge 11 is shown in FIGS.3A and 3B. This "thermally activated cutting" edge is accomplished byhaving heating element 12 heat the issue to weaken its structure. Theweakened tissue may then be severed by a relatively blunt instrumentcompared to the mechanically sharp surgical edge required to severtissue at body temperature. The preferred cutting edge of the presentinvention has a taper angle, theta, at the apex of heating element 12,in the range of approximately 15° to 50°, and more preferably, 20° to40°. The cutting edge comprises material having hardness, as measured bythe Rockwell Hardness Method, of less than about 40 Rockwell C. Such anedge, when heated to temperatures in excess of approximately 260° C.,produces a precise incision through tissue, but is not hard enough to beground with an edge sufficiently sharp to cut tissue at bodytemperature. Furthermore, instruments constructed in accordance withthis feature of the present invention may be conveniently bent andconfigured during surgery, by the surgeon, to reach tissue regions nototherwise accessible.

Referring now to FIG. 4, an alternative embodiment 20 of the presentinvention is described. Endoscopic instrument 20 is similar in otherrespects to endoscopic instrument 10 shown in FIGS. 1-3, except for theaddition of heater support member 27 interposed between heating element22 and elongated shaft 28. Thus, endoscopic instrument 20 includeselongated shaft 28, electric leads 24 and 26, terminals 23 and 25, andpotting material 29. The instrument may also include a tapered edge 21for providing thermally-enhanced cutting.

Heater support member 27 is composed of a low thermal conductancematerial for limiting heat conduction from heater element 22 to theelongated shaft. Heater support member 27 reduces heating of the distalportion of elongated shaft 18, and thereby reduces the likelihood ofheating tissue remote from the surgical site.

In accordance with the present invention, heater support member 27furthermore does not itself generate heat due to the AC current thatpasses through it. As discussed above, it is desirable to confine andlocalize the high temperatures present in heating element 22 so as tonot inadvertently damage or heat non-operative tissue. Thus, it isdesirable to be able to maintain heater support member 27 and elongatedshaft 28 at temperatures below approximately 60°-70° C. even when heaterelement 22 is at maximum operating temperature. Heater support member 27has low thermal conductance and does not dissipate significantelectrical power as current is conducted through it (i.e., has lowelectrical resistance). Thus, under these conditions, heater supportmember 27 stays at relatively low temperatures, compared to thoseexperienced by heating element 22.

A preferred material for heater support member 27 comprises a lowthermal conductivity nonferromagnetic metal or alloy such as stainlesssteel, for example, TYPE 304 stainless steel. The use of nonferromageticalloys or metals in heater support member 27 allows the AC currentpassing to be conducted throughout substantially the entire crosssection of the heater support.

Heater support member 27 may be connected to heater element 22 by anymethod that results in a low electrical resistivity junction. Suchmethods include thermally inert gas welding (TIG) and, more preferably,electron beam welding or laser-assisted welding.

FIGS. 5 and 6 show a "serpentine" embodiment 30 of a heating elementconstructed in accordance with the present invention, wherein the"serpentine" heating element 32 is disposed at an angle beta to thelongitudinal axis of elongated shaft 38. Angle beta is selecteddepending upon the type of endoscopic procedure to be employed, and maybe, for example, 30 degrees. Heating element 32 is attached to elongatedshaft 38 via low thermal conductance heater support member 37 thatconfines the heat generated in heating element 32 to the workingsurface. This embodiment provides an increased working surface area incomparison to the heating elements of FIGS. 1-4, as may be desirable forperforming surgical procedures such as cauterization of tissues in thetreatment of endometriosis. "Serpentine" heating element 32 may alsoinclude alumina cement 32a, or other similar material, to fill the airgaps between the scrolls of the heating element to provide a smooth,easy-to-clean surface.

As described hereinabove, the embodiments of the present invention ofFIGS. 4-6, include a "heater support member" interposed between theheating element and the distal end of the elongated shaft. As discussedabove, the heater support member reduces the leakage of heat from theheater element to the instrument shaft and is therefore fabricated froma material having a lower thermal conductance than the materialcomprising the heating element. Thus, the embodiments of FIGS. 4 to 6may be referred to as "dual-metal" embodiments.

Referring now to FIGS. 7-9, preferred embodiments of monolithic heatingelements of the present invention are described. Endoscopic heatingelement 40 of FIGS. 7A and 7B, includes auto-regulating metal substrate42, overlayer 44, optional taper 48 (see FIGS. 8A and 8B) and optionalnon-stick coating 46 (see FIGS. 9A and 9B).

Auto-regulating metal substrate 42 comprises a ferromagnetic material,or other material which undergoes a similar transition in currentconduction properties, when the temperature of the material varies.Suitable materials for use in heating element 40 are describedhereinbefore with respect to the embodiments shown in FIGS. 1-6.

Auto-regulating metal substrate 42 has a high-temperature workingsurface region 42a and a low-temperature region 42b. An AC electricpotential placed across terminals 43a and 43b in low-temperature region42b causes an AC electric current to flow between terminals 43a and 43band thus, through high-temperature working surface region 42a. Terminals43a and 43b are separated by an isolation air gap 47, which electricallyisolates terminal 43a from 43b, and which forces the AC current flowingthrough heating element 40 to conduct around loop 49 in high-temperatureworking surface region 42a. Isolation air gap 47, as was the case withthe "serpentine" heating element shown in FIG. 6, may also be filledwith alumina cement or other similar material to provide a smootheasy-to-clean surface. In accordance with the present invention, the ACcurrent is conducted within the skin-depth of substrate 42 inhigh-temperature working surface region 42a and around loop 49. Theresulting power dissipation heats region 42b to high temperaturessufficient to cause hemostasis of tissue and, if desired,thermally-enhanced cutting of the tissue (FIGS. 8A and 8B).Auto-regulation of the temperature of high-temperature working surfaceregion 42a is achieved by constructing region 42a of auto-regulatingmetal, such as a ferromagnetic metal or the like, as discussed abovewith respect to the embodiments of the endoscopic instrument shown inFIGS. 1-6.

As for the previously-described embodiments, auto-regulating metalsubstrate 42 may be configured in a variety of shapes, depending uponthe application of the particular endoscopic instrument. As describedhereinbefore, substrate 42 may be constructed using a variety of methodsand may include a thermally-enhanced cutting edge (FIGS. 8A and 8B).

Low-temperature region 42b of substrate 42 is covered with overlayer 44,a material that confines the heat generated in high-temperature workingsurface region 42a to the working surface area of the endoscopicinstrument. Overlayer 44 may comprise a nonferromagnetic metal or alloyhaving a low thermal conductance and thus serves the same purpose as theheater support member discussed above with respect to dual-metalembodiments shown in FIGS. 4-6. However, in contrast to the embodimentsof FIGS. 4-6, the low thermal conductance region is not separatelywelded or otherwise connected to the heating element 40. Thus, theembodiment of FIG. 7 comprises a monolithic heating element.

To reduce resistive heating of overlayer 44 caused by the AC currentpassing therethrough, the material comprising the overlayer should havea low electrical resistance in addition to low thermal conductance.Because of this preference for both low thermal conductance and lowelectrical resistance of overlayer 44, the selection of suitablematerials for the overlayer may involve trade-offs with respect to thethickness, length and composition of the overlayer.

For example, since different metals and alloys have different values forboth thermal conductivity and electrical resistivity, one metal may givelow electrical resistance, but have high thermal conductance. Thermalconductance is proportional to the geometrical area and inverselyproportional to the length of the thermal conductor, while electricalresistance has an opposite behavior (i.e., electrical resistance isinversely proportional to area and proportional to length). Thus,decreasing the thermal conductance of overlayer 44, by, for example,decreasing the cross-sectional area or increasing length of theoverlayer metal, may have the opposite effect on electrical resistance(i.e., electrical resistance will increase).

Accordingly, the geometry and composition of overlayer metal will dependupon the particular working surface shape that is employed for theauto-regulating substrate metal, and the intended application of theresulting endoscopic instrument. For example, in applications where itis not critical to localize the high temperatures in the heatingelement, for a given geometry it may be desirable to select a materialbased on its resistivity, rather than its thermal conductivity.Conversely, it may be desirable to trade higher electrical resistancefor lower thermal conductance in applications where it is more criticalto be able to localize the high temperatures of the heating element.

It will be apparent to one skilled in the art that once the particularapplication for the endoscopic instrument has been decided, and theshape and heating requirements of the heating element have beenestablished, the type and geometry of the particular overlayer metal canbe determined. These parameters may be chosen either experimentally, forexample, by measuring the localization of the heat (i.e., temperature asa function of distance along the endoscopic instrument), or by acombination of theoretical calculations and experimental measurements.Theoretical estimates may be obtained using conventional macroscopicsteady-state equations for electrical resistance (i.e., ElectricalResistance=Resistivity×[Length/Area]) and thermal conductance (i.e.,Thermal Conductance=Conductivity×[Area/Length]). Because the heatingelement is only heated for a few seconds at a time, the transfer of heatfrom the heating element to the low temperature region 42b may not reachsteady-state, however, the use of these theoretical calculations, willfor most cases provide adequate estimates of the performancecharacteristics of the heating element.

Preferably, the thickness of overlayer 44 should be thin enough so thatelectric current conducts throughout its entire cross-sectional area(i.e., the skin depth is many times its thickness) and thus the electricfields penetrate into the underlying auto-regulating metal substrate.

Overlayer 44 may comprise any metal or alloy that meets the desirablethermal conductance and electrical resistance characteristicsrequirements discussed above. Overlayer 44 may be disposed onauto-regulating metal substrate 42 using any technique capable ofachieving a low electrical resistivity junction and intimate thermalcontact with auto-regulating metal substrate 42, such as electroplating.Since plating thickness, produced by electroplating, is normallydirectly proportional to plating time, it may be advantageous to employmaterials requiring thinner thicknesses to reduce the cost of theendoscopic instrument.

Metals fulfilling the above requirements include, among others, nickeland copper. For the particular embodiment of endoscopic instrument shownin FIGS. 7-9, and having auto-regulating substrate 42 comprising an18-mil-thick alloy of iron and nickel, satisfactory performance has beenobtained using overlayer 44 of electroplated copper, approximately 0.125to 0.15 mil thick.

In FIGS. 8A and 8B, an alternative embodiment of a monolithic heatingelement similar to FIGS. 7A and 7B is described, in which an optionaltapered edge 48 is incorporated into heating element 40 to providethermally-enhanced cutting. Tapered edge 48 is constructed in accordancewith the principles hereinbefore discussed with respect to the otherembodiments of the heating elements shown in FIGS. 1-6.

Additionally, whether or not a tapered edge 48 has been incorporatedinto the endoscopic instrument, heating element 40 may also be providedwith a non-stick coating 46 for reducing the accumulation of coagulum onthe working surface, as shown in FIGS. 9A and 9B. Non-stick coating 46is provided in accordance with the principles hereinbefore discussedwith respect to the other embodiments of the heating elements shown inFIGS. 1-6. Additionally, in the preferred embodiment, non-stick coating46 covers high-temperature working surface region 42a completely.Furthermore, if isolation air gap 47 is filled with an alumina cement orother similar material, the non-stick coating may also cover the cementto provide an easy-to-clean surface. As shown in FIGS. 9A and 9B,non-stick coating 46 covers only a portion of low-temperature region 42b(see transition region 41 in FIGS. 9A and 9B). Preferably, transitionregion 41 is placed inside the elongated shaft which heating element 40would be disposed from. This reduces the exposure of non-coated materialto tissue during surgery.

In the embodiments of the endoscopic instrument described above withreference to FIGS. 1-9, the heating element was shown to be"permanently" attached to the elongated shaft. In accordance withanother feature of the present invention, there is provided anendoscopic instrument which includes a reusable universal handle whichis capable of accommodating a wide variety of disposable workingsurfaces wherein a used working surface can be easily removed from thehandle and replaced with a new or differently shaped working surface.

The above disposable working surface embodiment of the present inventioneliminates the need to re-sterilize the working surface after eachuse--it is simply disposed of after use. Furthermore, it eliminates theneed to employ a separate instrument for each type or configuration ofworking surface--one handle can accommodate a wide variety of workingsurfaces. It also allows a user to quickly interchange working surfacesduring endoscopic surgery without the need to also change instrumenthandles or power supply connections. Thus, it can also save surgery timeon the part of the user.

Referring the FIGS. 10-12, an illustrative embodiment of endoscopicinstrument 50 including a disposable working surface is described.Endoscopic instrument 50 includes elongated shaft 52 and disposableworking tip 54. Disposable working tip 54 is electrically energized asdescribed hereinabove through heating element electrodes 56A and 56B.

As shown in FIGS. 10A, 10B and 11, disposable working tip 54 includesauto-regulating heating element 56 (similar to that described above withrespect to FIGS. 8-9), end cap 58 and locking tongue 60. Elongated shaft52 is designed to mate with disposable working tip 54. Accordingly,elongated shaft 52 includes receptacle 62 and locking window 64 whichare adapted to provide a stable fit with disposable working tip 54.Receptacle 62 includes tongue insertion slot 63 (adapted to mate withlocking tongue 60) and electrode insertion slots 65A and 65B (adapted tomate with heating element electrodes 56A and 56B, respectively).

In accordance with the present embodiment, endoscopic instrument 50includes optional tube 66 extending from receptacle 62 of elongatedshaft 52. Tube 66 is intended to provide irrigation, or in thealternative, suction, during surgery. As shown in FIGS. 12A and 12B,tube 66 is adapted to fit into and through opening 68 in end cap 58 inorder to facilitate irrigation or suction.

Tube 66 is preferably made from a material capable of withstanding theworking temperatures experienced by heating element 56 and theconditions encountered during steam-sterilization procedures.Preferably, tube 66 is made from copper, brass, stainless steel or ahigh temperature plastic material. It will be apparent that irrigationor suction tube 66 could also be incorporated into any of theembodiments of endoscopic instruments discussed above with respect toFIGS. 1-9.

In addition to providing irrigation or suction during surgery, tube 66facilitates the attachment of disposable working tip 54 to elongatedshaft 52. Because tube 66 extends from receptacle 62 it allows a user toorient receptacle 62 with respect to working tip 54 without the need toparticularly identify tongue insertion slot 63 prior to an attempt toinsert locking tongue 60 into slot 63. This self-orienting featurefascilitates attachment of disposable working tip 54 onto elongatedshaft 52.

For surgical applications where endoscopic instrument 50 does not need atube for irrigation or suction, tube 66 may be replaced, if desired,with a solid stub or other equivalent extending member to facilitate theorienting of receptacle 62 with working tip 54, as discussed above.

As shown in FIGS. 12A and 12B, locking tongue 60 is designed so that itinterengages with tongue insertion slot 63 and locking window 64. Afterinsertion of disposable tip 54 into receptacle 62, radial-outwardtension in locking tongue 60 causes surface 60A of locking tongue 60 tobecome substantially flush with outer surface 52A (FIG. 12B) ofelongated shaft 52. Furthermore, locking tongue 60 includes an overhangedge 60B that is adapted to engage beveled edge 52B formed in the distaltransverse edge of locking window 64. The above features associated withlocking tongue 60 prevent unintentional detachment of disposable tip 54from elongated shaft 52, especially during endoscopic surgery.

Disposable tip 54 is removed from elongated shaft 52 by depressingtongue 60 with one hand while simultaneously pulling tip 54 away fromreceptacle 62 with the other. Tongue insertion slot 63 includes a cavity63A into which surface 60C flexes when locking tongue 60 is depressedfor removal as can be seen in FIG. 12B.

In accordance with the present embodiment, end cap 58 and receptacle 62are preferably made from a non-conducting injection moldable plasticcapable of withstanding the temperatures produced by heating element 56during operation. Furthermore, because receptacle 62 is permanentlyattached to elongated shaft 52 and not disposable as is end cap 58,receptacle 62 preferably should also be able to withstand conditionsencountered during steam-sterilization procedures. More preferably, endcap 58 and receptacle 62 are made from polyetherimide or polysulfonematerials.

Receptacle 62 and end cap 58 are preferably attached to elongated shaft52 and heating element 56, respectively, using either locking pins (notshown) or adhesive. Of course, any other conventional attaching meansmay also be employed.

In accordance with the present invention, electrodes 56A and 56B areinserted, respectively, into electrode insertion slots 65A and 65B. Whenin locked and working position, electrodes 56A and 56B are electricallyinsulated from each other because receptacle 62 is made from anon-conducting material.

Electrode insertion slots 65A and 65B (FIGS. 12A and 12B) extendproximally inward along elongated shaft 52 to allow electrodes 56A and56B to electrically connect to respective electrode contacts 57 (onlyone shown in figures). FIGS. 13A and 13B show a preferred embodiment ofelectrode contact 57 in isolation. Electrode contact 57 includes a pairof opposing contact fingers 58 and 59 having associated curved edges 58Aand 59A, respectively. Curved edges 58A and 59A provide a tightmechanical and low resistance contact to electrodes 56A and 56B.

Electrode contact 57 includes a pair of electrode pins 57A and 57B onthe opposite end from fingers 58 and 59. Electrode pins 57A and 57A areadapted to be inserted into an electrode contact receptacle (not shown)positioned inside elongated shaft 52. In the alternative, electricalconnection to electrode contact 57 can be made by soldering wirethereto.

In order to provide the necessary spring force to facilitate a tightmechanical and low resistance contact to respective electrodes 56A and56B, electrode contact 57 preferably should be made from a metal capableof repeatedly exerting adequate spring force (for example, an alloy ofapproximately 2% beryllium and 98% copper). In addition, it ispreferable to coat or plate electrode contact 57 with a thin layer ofgold (for example, 0.020 mil) to provide a low resistance electricalcontact to electrodes 56A and 56B during repeated use. If desired, anintermediate layer of another metal can be used to assist in adheringthe gold to the electrode metal (for example, 0.005 mil of nickel whenthe above beryllium-copper alloy is used).

If desired, the above-discussed non-stick coating could also be employedwith the disposable working tip embodiment of the present invention.

Thus, it is seen that various embodiments of an instrument forendoscopic surgery have been provided. The instrument has a heatingelement with a working surface for providing hemostasis to tissue at anauto-regulated temperature. The working surface may also include atapered edge for providing thermally-enhanced cutting of tissue, anon-stick coating for operating the instrument at low auto-regulationtemperatures, or both. Processes for making such instruments have alsobeen described.

In accordance with an additional aspect of the present invention, it isdesirable that endoscopic instruments with auto-regulating heatingelements are powered by a power source (see power source 9 in FIG. 1)that is capable of delivering a selectable and controlled amount ofcurrent to the heating element. The use of such selectable andcontrollable current, in combination with the auto-regulating heatingelement of the present invention, produces an endoscopic instrument withsubstantially stable temperature regulation, even after the activatedheating element contacts colder tissue. In use, the high frequencycurrent level is selected to elevate the heating element above it'sauto-regulation temperature in the range of the Curie transition of theheating element. As the heating element contacts tissue and cools belowthe auto-regulation temperature, the skin depth decreases and, underconstant current conditions, the amount of resistance heating increases.

A preferred power source capable of delivering a selectable andcontrollable current is described in commonly-assigned, co-pending U.S.patent application Ser. No. 07/877,454. This power supply is capable ofdelivering a substantially constant current level.

One skilled in the art will appreciate that the present invention can bepracticed by other than the described embodiments, which are presentedfor purposes of illustration and not of limitation, and the presentinvention is limited only by the claims which follow.

What is claimed is:
 1. A disposable working tip for use inendoscopically manipulating and coagulating tissue, the disposableworking tip adapted to be removably connected to the end of a reusableelongated shaft, the disposable working tip comprising:a working endhaving a working surface for contacting tissue and a cross-sectionextending perpendicularly to the working surface, the working endintegrally formed of a heating element, the working surface maintainedat an auto-regulated temperature by conducting a current throughout theentire cross-section of the working end, the heating element comprisinga material having a skin depth extending substantially throughout thecross-section of said working end responsive to the temperature of theheating element and that decreases as the temperature of the heatingelement falls below the auto-regulated temperature; first and secondterminals electrically coupled to the working end and adapted to beremovably coupled to the end of the reusable elongated shaft; and meansfor coupling the disposable working tip to the end of the reusableelongated shaft.
 2. A disposable working tip as defined in claim 1wherein the material further comprises a material that exhibits a Curietransition in permeability.
 3. A disposable working tip as defined inclaim 2 wherein the material further comprises a ferromagnetic material.4. A disposable working tip as defined in claim 1 wherein the workingsurface further comprises a tapered edge for thermally-enhanced cuttingof tissue at a temperature in the range of the auto-regulatedtemperature.
 5. A disposable working tip as defined in claim 4 whereinthe tapered edge defines an apex having an angle in the range ofapproximately 15 to approximately 50 degrees.
 6. A disposable workingtip as defined in claim 1 wherein the working end further comprises amaterial that can be bent and configured during surgery in order toreach tissue otherwise difficult to access.
 7. A disposable working tipas defined in claim 1 wherein the working surface further comprises acoating of electrically-insulating non-stick material to reduce theaccumulation of coagulum on the working surface.
 8. A disposable workingtip as defined in claim 1 further comprising:an end cap having apassageway therethrough adapted to permanently hold the working end; andengagement means disposed on said end cap for removably attaching saiddisposable working tip to said end of the reusable elongated shaft.
 9. Adisposable working tip as defined in claim 8 wherein the reusableelongated shaft includes a portion defining a window and said engagementmeans includes a locking tongue adapted to interengage the window.
 10. Adisposable working tip as defined in claim 8 wherein said end capincludes a second passageway for allowing a tube to pass therethrough,said tube being permanently disposed from the end of the reusableelongated shaft.
 11. A disposable working tip as defined in claim 10wherein the tube is adapted to provide irrigation during surgery.
 12. Adisposable working tip as defined in claim 10 wherein the tube isadapted to provide suction during surgery.
 13. An instrument for use inendoscopically manipulating and coagulating tissue comprising:a reusableelongated shaft having a proximal end and a distal end, the proximal endhaving first and second electrical connectors adapted to be coupled to apower supply; and a working end having a working surface for contactingtissue and a cross-section extending perpendicularly to the workingsurface, the working end integrally formed of a heating element, theworking surface maintained at an auto-regulated temperature byconducting a current throughout the entire cross-section of the workingend, the heating element comprising a material having a skin depthextending substantially throughout the cross-section of the working endresponsive to the temperature of the heating element and that decreasesas the temperature of the heating element falls below the auto-regulatedtemperature; first and second terminals electrically coupled to theworking end and adapted to be coupled to the first and second electricalconnectors, respectively; and means for removably coupling the workingend to the distal end of the reusable elongated shaft.
 14. An instrumentas defined in claim 13 wherein the material further comprises a materialthat exhibits a Curie transition in permeability.
 15. An instrument asdefined in claim 14 wherein the material further comprises aferromagnetic material.
 16. An instrument as defined in claim 13 whereinthe working surface further comprises a tapered edge forthermally-enhanced cutting of tissue at a temperature in the range ofthe auto-regulated temperature.
 17. An instrument as defined in claim 13wherein the working end further comprises a material that can be bentand configured during surgery in order to reach tissue otherwisedifficult to access.
 18. An instrument as defined in claim 13 whereinthe working surface further comprises a coating ofelectrically-insulating non-stick material to reduce the accumulation ofcoagulum on the working surface.
 19. A disposable working tip as definedin claim 13 further comprising:an end cap having a passagewaytherethrough adapted to permanently hold the working end; and engagementmeans disposed on said end cap for removably attaching said disposableworking tip to said end of the reusable elongated shaft.
 20. Aninstrument as defined in claim 19 wherein the reusable elongated shaftincludes a portion defining a window and said engagement means includesa locking tongue adapted to interengage the window.
 21. An instrument asdefined in claim 19 wherein said end cap includes a second passagewayfor allowing a tube to pass therebetween, said tube being permanentlydisposed from the distal end of the reusable elongated shaft.
 22. Aninstrument as defined in claim 21 wherein the tube is adapted to provideirrigation or suction during surgery.
 23. A disposable working tip foruse in endoscopically manipulating and hemostatically cutting tissue,the disposable working tip adapted to be removably connected to the endof a reusable elongated shaft, the disposable working tip comprising:aworking end having a working surface for contacting tissue and across-section extending perpendicularly to the working surface, theworking end integrally formed of a heating element, the working surfacemaintained at an auto-regulated temperature by conducting a currentthroughout the entire cross-section of the working end, the workingsurface including an atraumatic edge that becomes capable of cuttingtissue when heated to a temperature in the range of the auto-regulatedtemperature, the heating element comprising a material having a skindepth extending substantially throughout the cross-section of saidworking end responsive to the temperature of the heating element andthat decreases as the temperature of the heating element falls below theauto-regulated temperature; first and second terminals electricallycoupled to the working end and adapted to be removably attached to theend of the reusable elongated shaft; and means for coupling thedisposable working tip to the end of the reusable elongated shaft.
 24. Adisposable working tip as defined in claim 23 wherein the materialfurther comprises a material that exhibits a Curie transition inpermeability.
 25. A disposable working tip as defined in claim 24wherein the material further comprises a ferromagnetic material.
 26. Adisposable working tip as defined in claim 23 wherein the atraumaticedge comprises a tapered edge defining an apex having an angle in therange of approximately 15 to approximately 50 degrees.
 27. A disposableworking tip as defined in claim 23 wherein the working end furthercomprises a material that can be bent and configured during surgery inorder to reach tissue otherwise difficult to access.
 28. A disposableworking tip as defined in claim 23 wherein the working surface furthercomprises a coating of electrically-insulating non-stick material toreduce the accumulation of coagulum on the working surface.
 29. Adisposable working tip as defined in claim 23 further comprising:an endcap having a passageway therethrough adapted to permanently hold theworking end; and engagement means disposed on said end cap for removablyattaching said disposable working tip to said end of the reusableelongated shaft.
 30. A disposable working tip as defined in claim 29wherein the reusable elongated shaft includes a portion defining awindow and the engagement means includes a locking tongue adapted tointerengage the window.
 31. A disposable working tip as defined in claim29 wherein said end cap includes a second passageway for allowing a tubeto pass therethrough, the tube being permanently disposed from the endof the reusable elongated shaft, the tube adapted to provide suction orirrigation.
 32. An instrument for use in endoscopically manipulating andhemostatically cutting tissue comprising:a reusable elongated shafthaving a proximal end and a distal end, the proximal end having firstand second electrical connectors adapted to be coupled to a powersupply; and a working end having a working surface for contacting tissueand a cross-section extending perpendicularly to the working surface,the working end integrally formed of a heating element, the workingsurface maintained at an auto-regulated temperature by conducting acurrent throughout the entire cross-section of the working end, theworking surface including an atraumatic edge that becomes capable ofcutting tissue when heated to a temperature in the range of theauto-regulated temperature, the heating element comprising a materialhaving a skin depth extending substantially throughout the cross-sectionof the working end responsive to the temperature of the heating elementand that decreases as the temperature of the heating element falls belowthe auto-regulated temperature; first and second terminals electricallycoupled to the working end and adapted to be coupled to the first andsecond electrical connectors, respectively; and means for removablycoupling the working end to the distal end of the reusable elongatedshaft.
 33. A disposable working tip as defined in claim 32 wherein thematerial further comprises a material that exhibits a Curie transitionin permeability.
 34. A disposable working tip as defined in claim 33wherein the material further comprises a ferromagnetic material.
 35. Adisposable working tip as defined in claim 32 wherein the atraumaticedge comprises a tapered edge defining an apex having an angle in therange of approximately 15 to approximately 50 degrees.
 36. A disposableworking tip as defined in claim 32 wherein the working end furthercomprises a material that can be bent and configured during surgery inorder to reach tissue otherwise difficult to access.
 37. A disposableworking tip as defined in claim 32 wherein the working surface furthercomprises a coating of electrically-insulating non-stick material toreduce the accumulation of coagulum on the working surface.
 38. Adisposable working tip as defined in claim 32 further comprising:an endcap having a passageway therethrough adapted to permanently hold theworking end; and engagement means disposed on said end cap for removablyattaching said disposable working tip to said end of the reusableelongated shaft.
 39. A disposable working tip as defined in claim 38wherein the reusable elongated shaft includes a portion defining awindow and the engagement means includes a locking tongue adapted tointerengage the window.
 40. A disposable working tip as defined in claim38 wherein said end cap includes a second passageway for allowing a tubeto pass therethrough, the tube being permanently disposed from the endof the reusable elongated shaft, the tube adapted to provide suction orirrigation.